On the Web, dirty tricks are everywhere. Last month, would-be visitors to 25 million popular Web pages were intentionally rerouted to and then stuck at pornography sites. The incident brought to light one of the annoying aspects of Web surfing: You cannot always go where you want and, if you are in a place you don't want to be, you cannot always get out easily.

Some side trips are the result of mistakes by surfers, but many are the work of Webmasters who bend and twist HTML code into trapping people in one spot like overeager used-car salesmen.

Sites that specialize in pornography are the most obvious practitioners of user manipulation.

The Federal Trade Commission filed an injunction against the parties responsible for last month's page-jacking case. One reason the agency took such aggressive action was that "there isn't a whole lot the consumer can do," said Paul H. Luehr, assistant director of marketing practices at the Federal Trade Commission. "They were deceptively driven to these sites and then held there against their will."

The F.T.C. has a form on its Web site (http://www.ftc.gov) and a toll-free number (1-877-FTC-HELP) for consumers to file complaints about misleading sites